Coating is one of the most important and cutting-edge processes of modern pharmacy. Under special equipment, the sugar or other film-forming materials are coated on the outer surface of pharmaceutical solid preparation according to particular process, to become one or several multi-functional protective layers with different thickness and flexibility tightly adhered to surface after drying; and this multi-functional protective layer is called coating.
For the oral dosage forms of pharmaceutically active compounds, such as tablets, in order to be given in the form of tablets, it is often required to mask the unpleasant taste of the pharmaceutically active compound, such as bitterness, besides, enhance the apparent properties of tablets, to make it easier to swallow and reduce the absorption of water or moisture. After the tablets absorb moisture, the activity of the pharmaceutically active ingredients may be decreased, or other adverse changes in the tablet structure may occur, or the appearance of the tablets is impaired. The film coating is a way of masking the taste. The film coating can be soluble in gastric juice, so it will not diminish the action of the pharmaceutically active compound, but have a sustained release effect.
Tablets, pills and granules are the three main dosage forms of pharmaceuticals. They are easy to use, easy to absorb and have good efficacy. However, these drugs are not stable during the storage and transportation; therefore, it is required to encapsulate coating agent on the surface of drugs. But the existing coating agents have low coating film strength, poor UV-protection and anti-discoloration functions, reducing the storage stability of drugs.